By 1991,NATO was in search of an ammunition that could replace the 110 year old 9x19mm Parabellum that was associated with many of the pistols and submachine guns used.Eventually the 5.7x28mm ammunition was the ticket and soon after that,The FN P90 and the pistol known as the FN Five-Seven,Were a couple of the first 2 weapons that could fire the new ammunition.